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Cyanobacteria is the only prokaryotic group that performs oxygenic photosynthesis. Anoxygenic photosynthetic bacteria use PSI- and PSII-like photosystems, which are pigment protein complexes for capturing light. [5] Both of these photosystems use bacteriochlorophyll. There are multiple hypotheses for how oxygenic photosynthesis evolved.
Sponges (phylum Porifera) have a large diversity of photosymbiote associations. Photosymbiosis is found in four classes of Porifera (Demospongiae, Hexactinellida, Homoscleromorpha, and Calcarea), and known photosynthetic partners are cyanobacteria, chloroflexi, dinoflagellates, and red and green (Chlorophyta) algae.
Cyanobacteria, which are prokaryotic organisms which carry out oxygenic photosynthesis, occupy many environmental conditions, including fresh water, seas, soil, and lichen. Cyanobacteria carry out plant-like photosynthesis because the organelle in plants that carries out photosynthesis is derived from an [4] endosymbiotic cyanobacterium. [5]
Photosynthesis is the main means by which plants, algae and many bacteria produce organic compounds and oxygen from carbon dioxide and water (green arrow). An autotroph is an organism that can convert abiotic sources of energy into energy stored in organic compounds , which can be used by other organisms .
Photoheterotrophs generate ATP using light, in one of two ways: [6] [7] they use a bacteriochlorophyll-based reaction center, or they use a bacteriorhodopsin.The chlorophyll-based mechanism is similar to that used in photosynthesis, where light excites the molecules in a reaction center and causes a flow of electrons through an electron transport chain (ETS).
Ecosystems return this carbon through animal respiration, and plant respiration. [4] This constant cycle of carbon through the system is not the only element being transferred. In animal and plant respiration these living beings take in glucose and oxygen while emitting energy, carbon dioxide, and water as waste.
Cyanobacteria photosystem II, dimer, PDB 2AXT. Photoinhibition occurs in all organisms capable of oxygenic photosynthesis, from vascular plants to cyanobacteria. [14] [15] In both plants and cyanobacteria, blue light causes photoinhibition more efficiently than other wavelengths of visible light, and all wavelengths of ultraviolet light are more efficient than wavelengths of visible light. [14]
Oxygenic photosynthesis only evolved once (in prokaryotic cyanobacteria), and all photosynthetic eukaryotes (including all plants and algae) have acquired this ability from endosymbiosis with cyanobacteria or their endosymbiont hosts.